One of the most exciting moments in a prenatal ultrasound session is learning the sex of the baby.Following a conversation analysis perspective, we present a multimodal analysis of sequences of interaction between patient and practitioner at the time the foetus’ sex is the focus of attention. Based on video data collected from maternity wards and private practitioners, we report on two types of sequences, which illustrate the different ways of responding to the perceptually-occasioned formulation of the foetus’ sex: as a telling or as a noticing (in which case participants orient towards jointly seeing). While the possibility of both response is inherent to the sequential properties of noticing-based claims in general, we will discuss how the production of both types of sequences is sensitive and articulated to the distribution of epistemic authority as a practical achievement in this medical setting, along two dimensions: expert versus ordinary knowledge, and professional vision versus lay gaze.